Welcome, Nancylee. I've been taking Mestinon for years. When I first started, back in the mid 70's, my neuro told me to start taking 1/4 tablet of Mestinon at a time, every 4 hours. Then the next day I was to increase the dosage by 1/4 tablet, taking 1/2 tab at a time, every 4 hours. Then the next day up another 1/4, so I was taking 3/4 of a tablet. I was to increase by 1/4 tablet increments UNTIL I got symptoms of overdose. When that happened, I was to drop down 1/4 tablet, and fix that slightly lower dosage as my optimum dose.
You might try that, since it is very dificult for a neuro to just tell you how much mestinon to take. Everyone of us is so different, and what is the optimum dosage one day may turn out to be not quite enough or slightly too much the next day.
Also, there is an antidote you can keep on hand for overdose symptoms. The one my Dr prescribes for me is Donnatal. It contains Atropine, which is an antidote for Mestinon. Of course, it shouldn't be used to deliberately mask symptoms of overdose, but rather to relieve symptoms of overdose on the occasions when you forgot to take your Mestinon with food or maybe took a pill too soon.
And like redtail says, take your Mestinon with food. Hope things turn out well for you.